Cutting tools, in particular tools for metal-removing machining, consist of a main body which is made for example of hard metal, cermet, ceramic, steel or high-speed steel. To increase the tool life or to improve the cutting properties, a single-layer or multi-layer wear protection coating made of hard materials is frequently applied to the main body by means of CVD or PVD processes. The PVD processes come in a number of different variants such as magnetron sputtering, arc vapour deposition (arc PVD), ion plating, electron beam vapour deposition and laser ablation. Magnetron sputtering and arc vapour deposition are the PVD processes which are used most often for coating of tools. Individual PVD process variants in turn include a variety of modifications such as for example unpulsed or pulsed magnetron sputtering and unpulsed or pulsed arc vapour deposition, etc.
The target in the PVD process can consist of a pure metal or a combination of two or more metals. When the target comprises a plurality of metals, all these metals are incorporated at the same time into the coating layer built up during the PVD process. When the targets are composed of a mixture of metals, the quantitative ratio of the metals in the layer that is built up is essentially determined by the quantitative ratio of the metals in the target.
To produce certain metal compounds, the reaction chamber of the PVD process is supplied with reactive gases such as for example nitrogen to produce nitrides, oxygen to produce oxides, carbon-containing compounds to produce carbides, or mixtures of these gases to produce corresponding mixed compounds such as carbonitrides, oxycarbides, etc.
WO 96/23911 A1 describes a wear protection coating on a substrate, consisting of a layer of hard material applied directly on the substrate and over it a sequence of from 10 to 1000 further individual layers which consist in alternation of a metal hard material and a covalent hard material with the individual layers having a thickness of between 1 and 30 nm. The periodically alternating arrangement of individual layers of metal hard materials and covalent hard materials is designed to improve the mechanical and chemical properties of the wear protection coating.
WO 2006/041367 A1 describes a coated cutting tool consisting of a hard metal substrate and a coating deposited by the PVD process comprising at least one layer of TiAlN with a thickness of from 1.5 to 5 μm and an internal compression stress of >4 to 6 GPa. The layer of TiAlN is designed to exhibit improved adhesion to the substrate compared with known layers.
EP 2 298 954 A1 describes a method for producing a coated cutting tool on which a coating of hard material, such as for example TiAlN, TiAlCrN or TiAlCrSiN, is applied to a substrate by means of a PVD process, varying the bias voltage of the substrate during the deposition process. The method is designed to give the tool improved wear resistance and a longer life.
EP 1 992 717 describes a target for deposition of a layer of hard material by the PVD process which can contain Ti, Al, Cr, Si, B, C and N within different quantitative ranges.
EP 1 174 528 describes a cutting tool with a multi-layer wear protection coating which comprises a first layer of hard material and a second layer of hard material, the first layer of hard material containing one or more of the metals Ti, Al and Cr and one or more of the non-metals N, B, C and O and the second layer of hard material containing Si and one or more of the metals of the groups 4a, 5a and 6a of the Periodic System and Al and one or more of the non-metals N, B, C and O.
Particularly high demands are made on the tool for certain metal machining operations such as milling and turning for example. Important parameters for such tools are high temperature stability, high hardness, high fracture toughness and a high modulus of elasticity (E-modulus, Young's modulus).
Cutting tools and their wear protection coatings are usually designed for certain applications, and compromises normally have to be made as regards the properties named above when they are essential for the application as not all the desired properties can be optimised at the same time. Therefore there is a need for further improvement in the properties of wear protection coatings which are important for certain applications.
Known Ti85Si15N layers in wear protection coatings have for example very high hardness and very high E-moduli but comparatively poor tribochemical properties at high temperatures. Much the same is true of Al70Cr30N layers. In contrast to these, Ti50Al50N layers exhibit better tribochemical behaviour at high temperatures but lower hardness and lower E-moduli.